This invention relates to catalytic conversion of heavy, hydrogen-deficient, high metals content feedstocks to lower boiling liquids. It particularly relates to highly dispersed hydrogenating and/or cracking catalysts and methods for preparation thereof.
A great demand continues for refinery products, particularly gasoline, fuel oils, and gaseous fuels. Because of the shortage and cost of high quality petroleum-type feedstocks, the refiner now must obtain increased conversions of the heavier, more hydrogen-deficient, high impurity-containing portions of petroleum type feedstocks. Included in this category are heavy vacuum gas oils, atmospheric residua, vacuum tower bottoms, and even syncrudes derived from coal, oil shale, and tar sands.
In some cases, high levels of nitrogen and sulfur constitute a serious problem in such refractory, high molecular weight material, particularly with reference to downstream processing and environmental and pollution limitations associated with the products. An even more difficult problem is posed by the presence of metallic impurities, such as nickel, vanadium, iron, etc. in heavy petroleum fractions. Such metals, commonly associated with porphyrin rings and asphaltenes in high molecular weight cuts, can cause serious engineering/hardware problems in catalytic cracking. As a catalyst is exposed to repeated cycles of reaction/regeneration in a fluid catalytic cracker (FCC), these metals are adsorbed and tend to build up with time and accumulate on the catalyst. They then cause dehydrogenation-type reactions, resulting in formation of very large amounts of coke and large amounts of H.sub.2 gas which may put a severe strain on the FCC unit regenerator air blower and the wet gas compressor capacity. Further, and very important, their presence is often associated with a serious loss of conversion and gasoline yield.
Particularly because such residual fractions can contain high percentages of heteroatoms and metals which do not easily allow processing in catalytic units, obtaining maximum conversion of atmospheric and vacuum residue fractions to higher value premium distillate liquids is a continuing challenge. To avoid the aforesaid difficulties with catalytic cracking in the presence of these heteroatoms and metals, the major conversion processes have been delayed coking and fluid coking of these feedstocks.
In coking processes, thermally induced cracking not only produces lower boiling liquids but also produces high amounts of gas and coke byproducts because of the uncontrolled nature of the thermal reactions. Improvements in the yield pattern can be affected by hydrotreating the coker feed prior to thermal reaction, but this approach is limited by the poor metal tolerance of conventional hydrotreating catalysts.
A single-step process that can achieve substantial conversion of residua and similar hydrogen-deficient, high impurity-containing cracking feedstocks to lower boiling liquids while minimizing coke yields and producing more high quality liquids having low metal and heteroatom contents, so that these high quality liquids can be conventionally processed in fluid catalytic crackers, would be highly advantageous. Many methods have been proposed for doing so, and it has been found that highly dispersed metals such as Mo, Ni, and Fe, which have hydrogenating activity in their sulfided state, are most effective as means to control thermally induced reactions that take place in a homogeneous phase at high temperature. In fact, when the catalytic metal is initially present as a soluble compound, a limiting and very high catalytic effectiveness is reached which allows as little as 200 ppm of metal to achieve maximum control of the thermal conversions. This result requires, however, that an oil-soluble organometallic catalyst precursor be used. Examples of such compounds include naphthenates, pentanedionates, octoates, and acetates of metals such as Mo, Co, W, Fe, and V. Such metal-organic compounds are, however, expensive, relative to the water-soluble inorganic salts in which such metals are commonly found in nature.
U.S. Pat. Nos. 1,369,013 and 1,378,338 relate to oil-dispersed catalysts which are typically a compound of a catalytic metal united to a very weak, organic acid in an oil, such as nickel oleate. The metal-organic compound, soluble in oil, may be reduced with hydrogen or decomposed by heat to form an "oilcolloid" in a state of almost infinite subdivision.
U.S. Pat. No. 2,076,794 describes oil-dispersed catalysts which are emulsified by non-toxic emulsifying agents, such as a sodium salt of oleanolic acid ursolic acid, or other sapogenin.
U.S. Pat. No. 3,622,497 discloses a catalytic slurry process for hydrofining resids. The catalyst is unsupported and is colloidally dispersed vanadium sulfide, such as tetravalent vanadium salts which are prepared in a phenolic solution that decomposes under operational conditions to form catalytic vanadium sulfide, the ratio of sulfur to vanadium being nonstoichiometric, at a ratio of 0.8:1 to 1.8:1. The solution is non-aqueous, the tetravalent vanadium salt being dissolved in a phenol or phenolic mixture, preferably coal tar or wood tar, containing large amounts of catechol and various pyrogallol derivatives. This solution is then mixed with a charge stock, and the mixture is commingled with hydrogen, heated, and reacted at temperatures of 225.degree.-500.degree. C. and at pressures of 500-5000 psig.
U.S. Pat. No. 4,149,992 describes a dispersion wherein a phosphorus-vanadium-oxygen catalyst is mixed and then heated to evaporate the water and form a putty which is extruded and then dried and calcined.
U.S. Pat. No. 4,252,671 discloses a method for preparing a homogeneous, physically stable dispersion of colloidal iron particles by preparing a solution of an active polymer in an inert solvent and incrementally adding thereto an iron precursor at a temperature at which the iron precursor becomes bound to the active polymer and thermally decomposes to produce elemental iron particles in an inert atmosphere. A polymer solution can be prepared from copoly(styrene/4-vinylpyridine) and water-free o-dichlorobenzene at room temperature. Iron pentacarbonyl is added in increments during very gradual heating until the iron pentacarbonyl is completely decomposed to form a dispersion after cooling at room temperature and under an inert atmosphere.
U.S. Pat. No. 4,252,677 describes a method for preparing homogeneous colloidal elemental dispersions of a catalyst in a non-aqueous fluid. A colloidal dispersion of nickel particles can be prepared with a hydroxyl-terminated copoly(styrene/butadiene) as the functional polymer. Using a similar dispersion of palladium particles, the polymer solution of copoly (styrene/4-vinylpyridine) can be formed by dissolving the copolymer in diethyleneglycoldimethyl ether.
Going beyond these patented processes, there nevertheless exists a need for a process of preparing a highly dispersed heterogeneous catalyst, which is colloidal or submicron in size, for the hydrothermal conversion of heavy oils and residua that can obviate the expense and processing difficulties associated with using organic reactants and that can incorporate the desired catalytic metals in their inorganic form.